The present invention relates to shaped magnetic poles for thin-film magnetic heads. More particularly, it relates to shaped magnetic poles which reduce undershoot in the information retrieval signal.
In magnetic recording devices, thin-film magnetic heads retrieve ("read") and store ("write") information to magnetic media by magneto-resistively or inductively sensing the magnetization of and creating respectively, localized magnetic domains in the media. When reading information from a magnetic medium, a thin-film head's interface surface moves over the medium at a short distance from the medium so that magnetic flux from the localized domains enters permeable material pole tips in the interface surface. This flux extends over a selected permeable material path from the surface of the pole tips at the interface surface to an electromagnetic transducer which converts the magnetic flux in the path into an electric read current. The electric read current is used by the recording device in which the head is mounted to create an electric read signal.
As the thin-film head approaches a new magnetic domain, flux from that domain extends through the leading edge of the closer of the two pole tips, creating a small magnitude pulse in the read signal. When the thin-film head crosses fully over the new domain, flux from that domain extends through both pole tips and over the permeable material path producing a large magnitude pulse in the read signal of opposite polarity to that of the first pulse. As the magnetic head exits the domain, a small amount of flux from that domain extends through the trailing edge of the last pole tip and creates a small magnitude pulse in the read signal of the same polarity as the first small pulse.
The large magnitude pulse is intermediate in time over the time it takes the head to cross over the domain and is the primary pulse in the read signal. The series of primary pulses in the read signal produced by the thin-film head as it moves over the series of magnetic domains in the medium is translated into binary data by decoding circuitry in the magnetic recording device. Ideally, the primary pulses obtained from each domain are large in magnitude so that they are easily detected by the decoding circuitry and narrow in width, i.e. short in time with respect to the domain crossing time, so that they do not interfere with one another. The two smaller pulses on either side of the primary pulse in time are termed "undershoots". Undershoots in the read signal are undesirable because they may overlap in time, i.e. "interfere", with primary pulses created by other magnetic domains. This interference, known as intersymbol interference, indirectly reduces the lineal density of the domains in the magnetic media because the linearly sequential domains must be positioned far enough apart so that undershoots from one domain do not interfere with the primary pulse of another domain in such a way that the primary pulses become undetectable.
The magnitude of undershoots in the read signal is affected by the geometry of the pole tips and specifically by the location and position of the edges of the pole tips. To remove undershoots, several methods have been developed which change the location and position of these edges. These methods mill away the edges of existing pole tips to create new pole tip shapes. Examples of these new pole tip shapes can be found in Ramaswamy, RECORDING HEAD TO MINIMIZE UNDERSHOOTS IN READBACK PULSES, U.S. Pat. No. 4,970,616, Issued Nov. 13, 1990; Howell, T. D. et al. "Advanced Read Channels for Magnetic Disk Drives", IEEE Transactions on Magnetics, vol. 30, no. 6 (November 1994), pp. 3807-3812; and Yoshida, M. "Edge Eliminated Head", IEEE Transactions on Magnetics, vol. 29, no. 6 (November 1993), pp. 3837-3839. Although these new pole tip shapes change the location and position of the pole tip edges, the pole tip shapes found in these references have manufacturing or performance characteristics which make them less than optimum for reducing undershoots in the read signal.